1. Field of the Invention
The present invention relates to an electrostatic lens included in a charged particle beam optical system used in an exposure apparatus using a charged particle beam.
2. Description of the Related Art
In electron beam exposure apparatuses, electron optical elements are used to control optical characteristics of an electron beam. An electron lens controls the beam diameter or the aberration of an electron beam. Electron lenses are classified into the electromagnetic type and the electrostatic type. Compared with electromagnetic electron lenses, electrostatic electron lenses need, for example, neither coils nor cores, achieving reduction in size and high integration easily. By using electrostatic lenses, an increase in the number of beams and high density can be easily achieved, resulting in an improvement in the throughput of an exposure apparatus and high resolution performance.
In Japanese Patent Laid-Open No. 2007-266525, a charged particle beam lens array is disclosed which is used for a multi-beam exposure apparatus and which is formed by bonding a silicon electrode plate and a glass spacer together. In Japanese Patent Laid-Open No. 2005-57110, a multi-charged beam lens is disclosed which is formed of spacers and electrodes, each of which is obtained by forming a gold thin film on silicon as a conductive film. In OSAMU YAMAMOTO et al., Charging and Flashover Characteristics of a Fused Quartz Spacer in Vacuum, IEEJ transactions on Fundamentals and Materials, pages 429-435, vol. 123, No. 5, Aug. 1, 2003, The Institute of Electrical Engineers of Japan, Tokyo, Japan (hereinafter, referred to as Non-Patent Document 1), characteristics of surface charging of a spacer which are obtained when a high voltage is applied to a gap of approximately several hundred micrometers to several millimeters are disclosed as experimental and theoretical research.
In positional control of an electron beam in an electrostatic lens including electrodes and an insulating spacer (hereinafter, simply referred to as a spacer), deflection of an electron beam may occur due to an influence of charging of the spacer disposed near a through hole of an electrode, through which the electron beam passes. Since the spacer is a supporting member for fixing the distance between the electrodes, the spacer needs to support the electrodes without distortion or the like. Accordingly, in order to achieve high resolution of an exposure apparatus, there has been an issue in which a spacer is to be disposed so as to fix the distance between electrodes disposed in a limited region, while reducing an influence on deflection of a beam. Typically, a silicon electrode is often used as an electrode in an electrostatic lens. However, in the case where a surface of the silicon electrode is oxidized, beam deflection may occur due to charging of the oxidized portion, in addition to beam deflection due to charging of a spacer.
To use an exposure apparatus stably, carbon contaminants or the like which are attached to an electrostatic lens in the exposure apparatus may be removed by oxygen plasma cleaning. Oxygen plasma cleaning causes oxidation of a surface of an electrode, resulting in an issue of suppression of displacement of the beam position caused by charging of the oxidized portion. A solution for preventing oxidation of an electrode is a protective film of a material, such as a noble metal or a conductive oxide, which is formed on the electrode. Typically, a configuration is employed in which a region close to a through hole is not oxidized. However, the relationship between deflection of a beam and the positions of the protective region of the gold thin film and the spacer is not always optimized.
In an electrostatic lens, it is important that corresponding ones of through holes of multiple electrodes are aligned with high precision, and that such a state is maintained. To achieve this, after positioning is performed, it is desirable that electrodes and spacers be integrated with each other by bonding so that a required strength is obtained. However, in the case where dust is to be removed from the inside by cleaning after the integration, it has been pointed out that such cleaning is difficult. In addition, in the case where a protective film is formed simply over a silicon electrode to prevent electrode oxidation, since the protective film is interposed at a bonding interface between the silicon electrode and a glass spacer, a problem arises in that stable bonding like bonding between silicon and glass is not achieved.
An example of the present invention may provide an electrostatic lens in which a protective film is disposed on an electrode and in which beam deflection due to charging is prevented. An example of the present invention may also provide an electrostatic lens which can achieve and maintain a high-precision positioning state of component members and which can also be easily handled.